The present invention relates generally to a paper feeding apparatus for printers, and, in particular, to an apparatus for feeding individual sheets of paper as well as continuous fanfolded paper utilizing a platen.
Conventional printers include a platen, a roller and a printhead. The roller has a diameter smaller than the diameter of the platen and is provided at the upper portion of the printhead located at the paper feed-out position relative to the printhead and platen. The roller is pressed against the platen with the paper being positioned therebetween to generate a frictional force to cause the fed-out portion of the paper to be drawn out after printing has occurred.
The paper feed speed at both the supply side of the printer and the feeding-out region are determined by the platen diameter. Accordingly, a platen having a uniform diameter is required so that no difference is caused between the paper input speed and paper output speed. No problem arises in feeding individual sheets of paper. However, when feeding continuous rolls of paper having a line of feeding holes spaced at regular intervals therebetween along both edges, such as in computer paper, where the power for feeding is not provided by the platen but rather by a sprocket or belt having pins inserted in the feeding holes, conventional printing results in inferior print quality and feeding. A fine difference between the speed of the platen and the speed of the sprocket arises due to the differences in ambient temperature and paper sag resulting in tearing of the feed holes ad other such problems when paper feeding is repeated over a long period of time corresponding to large distances of paper. Accordingly, in the conventional printer, high position accuracy of the paper with respect to the printhead and stable paper feeding over a long period of time cannot be maintained.
Additionally, the conventional printer includes a paper bail for pressing paper against the cylindrical platen. The paper bail is driven by a solenoid to a position in which the bail is in contact with the platen as well as to a position in which the bail is released from the platen. The paper bail, when not being driven by the kinetic energy of the solenoid, is either in touch with the paper on the platen or in touch with a stopper which is at a release position and held with mechanical shocks. The bail is supported on a paper bail lever and a loading lever. Accordingly, the conventional printer produces impact noises caused by the abrasion or impinging at a junction portion of a paper bail shaft with the paper bail lever or at a junction portion of the paper bail lever with a loading lever producing rasping. Furthermore, marks caused by the paper bail are left on pressure sensitive paper as a result of the impact of the paper bail when it is returned to the press position from the paper release position. Additionally, when a mechanical dampener is attached to lighten the impact of the paper bail, the device by necessity must become complicated and overly large. The mechanical dampener may be a solenoid with a shock absorbing member positioned between the movable core and fixed core. It may also be a solenoid having a gap on the absorbing surface between the movable core and fixed core for achieving an air dampener type operation which absorbs noises when the movable core is absorbed by the fixed core. The mechanical dampener may also include a solenoid having an external shock absorbing member.
Reference is now made to FIGS. 1, 1A, 2 wherein the structure and method for inputting and feeding out paper for a conventional controlling method and printer is provided.
The conventional printer is provided with a platen 55 and a paper feeding roller 58 pressing against platen 55 for feeding a sheet of paper 13 therebetween. A printhead 7 is spaced a predetermined distance from platen 55.
In a first step 101 (FIG. 2), the power of the printer is turned on. Print paper 13 is manually inserted so that the end of paper 13 is positioned at a position wherein paper feeding roller 58 is pressed against platen 55 in accordance with a step 102 and then is adjusted so that the top end of paper 13 is at position S in accordance with a step 103.
A switch 202 for autoloading paper 13 provided on an operation panel 200 or the like is then pressed in accordance with a step 104 causing platen 55 to rotate in the direction of arrow U a predetermined distance stored in a ROM 204 to feed the paper 13 in the direction of arrow P in accordance with a step 105. The loading sequence is completed when the leading edge of paper 13 originally at position S is fed to a predetermined starting position R. The print apparatus is now in a condition for awaiting for print data.
When individual cut sheets 13 are utilized, printing sometimes starts at a position which is not predetermined, for example, within a predetermined frame or at the very upper portion of paper 13. Accordingly, in the conventional printer, it becomes necessary to determine whether additional controlling of the feed amount is required in accordance with a step 106. In the conventional process, when additional positioning is required, the user turns a knob 206 or the like attached to the platen 55 to adjust the starting position of paper 13 after the paper positioning has been set by the autoloader in correspondence with a step 107. Step 107 is repeated until proper positioning is obtained. Accordingly, printing with a conventional printer necessitates fine adjustment of the starting position which is difficult since manual turning of the platen 55 is required. Since the platen 55 must be turned manually and since the knob 206 must be turned for the printing of each new paper sheet 13, the adjustment operation is troublesome and varies between different sized sheets. The printer then waits for the printing data to be input in accordance with a step 108 and when the printing data is received, it prints on paper 13 in accordance with a step 109 until the process is completed and ended in accordance with a step 110. Thus, paper loading in accordance with the prior art is cumbersome and difficult.
Accordingly, it is desired to provide a paper feeding apparatus for a printer which overcomes the disadvantages of the prior art devices described above.